Control system and method for walking drilling rigs

ABSTRACT

A method for moving a drilling rig includes receiving a selection of a rig walking mode, wherein the rig walking mode corresponds to a direction of movement, determining an angle of orientation for feet of the drilling rig based on the selected rig walking mode, rotating the feet such that the feet are in the angle of orientation, lifting the rig by pushing the feet into a ground, and moving the rig relative to the ground in the direction of movement.

BACKGROUND

Drilling rigs are machines that drill wells, e.g., oil and gas wells. A drilling rig may include a substructure that supports a floor and a mast over a well center. Drilling equipment is located on the floor and the mast, and is configured to run a drill string (including a drill bit, drill pipes, and potentially various other equipment) downward, thereby forming and extending the wellbore into the earth. Various equipment may be located below the rig floor, e.g., between bases boxes of the substructure.

In some situations, “pad drilling” is employed, in which several wells are drilled near to one another. Rather than using multiple drilling rigs, or assembling and disassembling the rig to move between wellsites, some rigs are self-ambulatory. These rigs are often referred to as “walking” rigs, and generally include feet that press down onto the ground (e.g., onto a mat that is laid on the ground), which lifts the substructure of the rig up. The feet are then moved linearly with respect to the ground, e.g., via rollers, slides, etc., across a range of motion, generally provided by a stroke of a hydraulic piston. At the end of the range, the rig is lowered back onto the ground, the feet are raised and moved back to the beginning of the range of motion, and the next “step” of the walking process may commence by again pressing the feet down onto the ground.

More recently, steerable walking rigs have been implemented. These rigs may allow the rig to walk in any direction in the horizontal plane. For example, the walking rigs may be configured to walk forward, backward, and sideways, and/or to rotate. However, rotating the rig can be complicated, because the feet move linearly, but rotation is along a circular path. Moreover, the rig is not perfectly rigid, but may deflect during such rotation. Thus, precise orientation of the feet may be called for, with accidental misalignment, e.g., by human error, presenting hazards for both the rig and personnel.

SUMMARY

This summary is provided to introduce a selection of concepts that are further described below in the detailed description. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in limiting the scope of the claimed subject matter.

Embodiments of the disclosure may provide A method for moving a drilling rig includes receiving a selection of a rig walking mode, wherein the rig walking mode corresponds to a direction of movement, determining an angle of orientation for feet of the drilling rig based on the selected rig walking mode, rotating the feet such that the feet are in the angle of orientation, lifting the rig by pushing the feet into a ground, and moving the rig relative to the ground in the direction of movement.

Embodiments of the disclosure may also provide a drilling rig system including a substructure, a plurality of walking pods coupled to the substructure, each of the walking pods including a rotating mechanism, a lift mechanism, a travel mechanism, and a foot. The rotating mechanism is configured to rotate the foot relative to the substructure and a ground, the lift mechanism is configured to raise and lower the foot relative to the substructure and the ground, and the travel mechanism is configured to move the foot relative to the substructure and the ground in a horizontal direction. The system also includes a control system in communication with the plurality of walking pods. The control system is configured to: receive a selection of a rig walking mode, the rig walking mode including a walking direction; cause the respective rotating mechanisms to rotate the respective feet, such that each foot of the walking pods is in a predetermined orientation; cause the respective lift mechanisms to lift the substructure by pushing the feet into the ground; and cause the travel mechanisms to move the substructure relative to the feet in the predetermined orientation.

Embodiments of the disclosure may further provide a method for moving a drilling rig. The method includes receiving a selection of a rig walking mode. The rig walking mode corresponds to a direction of movement, and the rig walking mode is selected from a plurality of rig walking modes. Each of the plurality of rig walking modes is associated with at least one angle of orientation for feet of the drilling rig. The method further includes determining a respective angle of orientation for each of the feet of the drilling rig based on the selected rig walking mode, rotating the feet such that each of the feet are in the respective angle of orientation, lifting the rig by pushing the feet into a ground, and moving the rig relative to the ground in the direction of movement.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the present teachings and together with the description, serve to explain the principles of the present teachings. In the figures:

FIG. 1 illustrates a perspective view of a portion of a substructure for a drilling rig, including walking pods that provide at least a part of a rig relocation system, according to an embodiment.

FIG. 2 illustrates a perspective view of a portion of a walking pod, according to an embodiment.

FIG. 3 illustrates a schematic view of a drilling rig relocation system, according to an embodiment.

FIG. 4 illustrates a flowchart of a method for controlling rig relocation operations, according to an embodiment

FIG. 5 illustrates a top, plan view of the drilling rig relocation system configured for moving the drilling rig in a first linear direction (forward/aft), according to an embodiment.

FIG. 6 illustrates a top, plan view of the drilling rig relocation system configured for moving the drilling rig in a second linear direction (side-to-side), according to an embodiment.

FIG. 7 illustrates a top, plan view of the drilling rig relocation system configured for rotating the drilling rig in a first circumferential direction (counterclockwise), according to an embodiment.

FIG. 8 illustrates a top, plan view of the drilling rig relocation system configured for rotating the drilling rig in a second circumferential direction (clockwise), according to an embodiment.

FIG. 9 illustrates a schematic view of a computing system for performing one or more portions of the method disclosed herein, according to an embodiment.

DETAILED DESCRIPTION

Reference will now be made in detail to specific embodiments illustrated in the accompanying drawings and figures. In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the embodiments described herein. However, it will be apparent to one of ordinary skill in the art that embodiments may be practiced without these specific details. In other instances, well-known methods, procedures, components, circuits, and networks have not been described in detail so as not to unnecessarily obscure aspects of the embodiments.

It will also be understood that, although the terms “first”, “second”, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are used to distinguish one element from another. For example, a first object could be termed a second object, and, similarly, a second object could be termed a first object, without departing from the scope of the present disclosure.

The terminology used in the description of the techniques herein is for the purpose of describing particular embodiments and is not intended to be limiting. As used in the description of the techniques herein and the appended claims, the singular forms “a,” “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will also be understood that the term “and/or” as used herein refers to and encompasses any and all possible combinations of one or more of the associated listed items. It will be further understood that the terms “includes,” “including,” “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. Further, as used herein, the term “if” may be construed to mean “when” or “upon” or “in response to determining” or “in response to detecting,” depending on the context.

FIG. 1 illustrates an isometric view of a drilling rig substructure 10, according to an embodiment. The substructure 10 may be integrated into a drilling rig for drilling a wellbore, e.g., including components such as a rig floor, mast, rotating equipment, pipe handling equipment, etc. In the illustrated embodiment, the substructure 10 includes a driller's side base box 12 and a parallel, off-driller's side base box 14. The base boxes 12, 14 may be connected together and held separate by a base box spreader 16, which may take the form of a K-brace, as shown. The wellbore that the fully-assembled drilling rig drills may be positioned between the offset base boxes 12, 14.

The drill rig substructure 10 may also include one or more relocation systems or “walking pods” 100 located at each end of base boxes 12, 14, e.g., at the four corners of the generally rectangular substructure 10. The walking pods 100 may each include a foot 102, a lift mechanism 104, and a rotation mechanism 106. For example, the lift mechanism 104 may be or include a hydraulic cylinder, which is configured to move the foot 102 up and down (e.g., away from and toward the ground). The rotation mechanism 106 may be a slew drive or another type of device that is configured to rotate the foot 102, e.g., about an axis extending vertically therethrough. The walking pods 100 may each additionally include a travel mechanism 108, such as one or more (e.g., a pair of) horizontally-oriented cylinders that are configured to move the foot 102 horizontally with respect to the ground, e.g., in a direction that depends on the rotational orientation set by the rotation mechanism 106. In some embodiments, the walking pods 100 may be movable independently of one another, as each may include an individual assembly of a foot 102, lift mechanism 104, rotation mechanism 106, and travel mechanism 108. Accordingly, the movement of the walking pods 100 may be coordinated to efficiently relocate the drilling rig.

FIG. 2 illustrates an enlarged, perspective view of one of the walking pods 100, according to an embodiment. In particular, FIG. 2 shows part of the foot 102, the lift mechanism 104, and the travel mechanism 108. By way of example, the travel mechanism 108 includes cylinders 201, 202 and slides 206 that are received around cylindrical members 204 coupled to the foot 102. Accordingly, when the cylinders 201, 202 stroke, the foot 102 is moved relative to the remainder of the pod 100.

Additionally, FIG. 2 shows the rotation mechanism 106, which is illustrated as including a motor (e.g., a hydraulic motor) 205, a slew drive 207, and a rotary position sensor (e.g., an encoder 208). The motor 205 turns a shaft (e.g., a screw or helical shaft), which engages gears on the slew drive 207 that cause the slew drive 207 to rotate the foot 102 relative to the remainder of the pod 100 (and the ground), which is stationary with respect to the base boxes 12, 14 (FIG. 1). The rotary encoder 208 measures the rotational displacement of the foot 102 by measuring the turning of the slew drive 207, e.g., by counting turns of the shaft thereof that is connected to the motor 205. In other embodiments, the rotary encoder 208 may directly measure the rotational displacement of the foot 102, e.g., relative to the lift mechanism 104, or in any other convenient manner.

The rotary encoder 208 may be electrically coupled to a controller, and may be configured to provide signal thereto representative of the rotational orientation of the foot 102 relative to the base boxes 12, 14. FIG. 3 illustrates a schematic view of such a drilling rig system 300, according to an embodiment. As shown, the drilling rig system 300 includes the pods 100 and a remote control device 302 (e.g., a mobile control module or “belly pack”), which may be in communication with one another. In some embodiments, as shown, a rig controller 304 may be interposed between the remote control device 302 and the pods 100 and may enable, disable, and/or implement commands from the remote control device 302 by controlling the pods 100. For example, the rig controller 304 may receive signals from the encoders 208 (FIG. 2) of the individual pods 100 and provide data representing an angular orientation of the associated foot 102 (FIG. 2) to the remote control device 302.

FIG. 4 illustrates a flowchart of a method 400 for controlling rig relocation operations, according to an embodiment. The method 400 may be implemented, e.g., using an embodiment of the drilling rig system 300 as discussed above; thus, for purposes of illustration, is described with reference thereto. However, it will be appreciated that various embodiments of the method 400 may be executed using other systems and/or structures. Furthermore, it will be appreciated that the following worksteps may be combined, separated into two, conducted in parallel, or conducted in a different order, without departing from the scope of the present disclosure.

The method 400 may begin by receiving a rig walking mode selection from the control device 302, as at 402. The rig walking mode may represent the “type” of walking of the rig 300 that may be desired, e.g., moving forward/aft, moving toward the driller-side or off-driller-side (e.g., left or right), rotate clockwise, or rotate counterclockwise.

In various embodiments, the control device 302 may also be configured to individually control the lift, rotary position, and/or linear position of the feet 102, which may give the operator the ability to position the feet 102 in any orientation desired. However, once a rig walking mode is selected at 402, the automated controls may take over control, and may lock or otherwise disable the control device 302 from controlling the individual pods 100, as at 404. It will be appreciated that various safety control interrupts and/or other mechanisms by which control may be returned to manual may be provided.

The method 400 may then include determining an angular orientation for the feet 102 based on the selected rig walking mode, as at 406. Referring now to FIG. 5, there is shown a first walking mode, in which, as indicated, the feet 102 are oriented to move parallel to a rig centerline 500, which extends forward and aft. As such, the feet 102 are oriented at 0 degrees from the base boxes 12, 14, as shown.

FIG. 6 illustrates a second rig walking mode, in which the feet 102 are oriented to move perpendicular to the base boxes 12, 14, i.e., toward the driller's side or off-driller's side (e.g., left and right, if the ends of the base boxes 12, 14 are considered the front and aft of the rig 300). As such, the feet 102 are oriented to 90 degrees from the centerline 500.

FIG. 7 illustrates a third walking mode, in which the rig 300 is rotated clockwise, as viewed from above. As described above, the pods 100 move the rig 300 by moving the rig 300 and feet 102 in a linear relationship, e.g., by stroking a horizontally-oriented piston. However, it may be desired to rotate the rig 300, which may call for the feet 102 to move along an arcuate path, which may not be available, because the rig/feet move along a linear path. One way to address is this referred as the “chord method,” in which, rather than moving tangent to the illustrated circle 700, the ends of the base boxes 12, 14 move between two points on the circle across an internal chord line. To follow such a chord, the feet 102 may be precisely oriented, and may be positioned at two or more angular orientations. For example, as shown, two of the feet 102A, 102B are oriented at a first angle, e.g., 60.6 degrees and two feet 102C, 102D are oriented at a second angle, e.g., 56.6 degrees. These angles are merely examples, and wide deviation therefrom may be implemented by one of skill in the art. For example, the first angle may be greater than the second angle by between about 1 degree and about 10 degrees. Further, in this illustration, a “right hand” rule is implemented, in which the angle is positive, sweeping in the counterclockwise direction, but any consistent regime for measuring angles may be implemented so as to accurately compare angles.

Similarly, FIG. 8 shows a fourth walking mode, in which the rig 300 is rotated counterclockwise. Again, the angles of the feet 102 are set so that the pods 100 move the ends of the base boxes 12, 14 through a chord in the circle 700, this time in the reverse circumferential direction.

Returning to FIG. 4, once the desired rig walking mode has been selected at 402, individual control of the pods 100 disabled (in some embodiments), and the angular orientation has been determined at 406, the method 400 may proceed to receiving a walk command from the control device 302, as at 408.

In response, the rig controller 304 may then proceed to automatically (without human intervention) rotating the feet 102 to the predetermined orientation, or substantially to the predetermined orientation (e.g., within a reasonable tolerance such as plus or minus 1 degree), according to the selected rig walking mode, as at 410. The feet 102 may be rotated in unison, in sequence, or in any combination thereof. In some embodiments, the rig control 304 may rotate the feet 102 upon receiving the walking mode selection at 402 (e.g., prior to receiving the walking command at 406). In other embodiments, as shown, the rig controller 304 may wait for the walk command before moving/rotating the feet 102.

Further, the encoder 208 may provide feedback to the rig control 304. In turn, the rig control 304 may determine when to stop the rotation of the feet 102, e.g., by signaling to the rotation mechanism 104. The rig controller 304 may also cause the remote control device 302 to display the individual orientations of the feet 102 to the operator, and thus the operator may serve as an additional safety check by reviewing the actual orientation of the feet 102. The encoder 208 may thus provide a feedback loop.

In some embodiments, the rotation of the feet 102 may implement a ramp function. For example, the rotation mechanism 106 may be hydraulically-operated, and the rotating portion of the pods 100 (including the feet 102) may carry a large amount of inertia; thus, precisely stopping at a predefined angle may be a challenge. To handle this challenge, the speed of the rotation mechanism 104 may be modulated depending on how much rotation is called for. Thus, in a situation where the direction changes a large amount (e.g., going from forward/aft walking to driller's side/off-driller's side walking), the rotation mechanism 106 may ramp up to moving quickly, and then slow down as the foot 102 approaches the end of the desired rotation. Further, in at least one embodiment, the rig controller 304 may use the feedback from the encoder 208 to display the current angular position of the feet 102 on the control device 302.

Once setting the feet 102 to the predetermined orientation, the method 400 may proceed to lowering the feet 102 and lifting the rig 300, e.g., using the lifting mechanism 104 discussed above, as at 412. Once the rig 300 is lifted, the travel mechanism 108 may be employed to move the rig 300 horizontally relative to the feet 102, as at 414. The consequence of this movement may be to move the rig 300 in a linear direction or to rotate the rig 300, as discussed above, depending on the rig walking mode implemented.

The method 400 may then include lowering the rig 300 and raising the feet 102, thereby setting the rig 300 back down on the ground, as at 416. With the weight removed from the feet 102, the feet 102 may be moved relative to the base boxes 12, 14, e.g., using the travel mechanism, such that the feet are prepared to travel walk the rig again in a subsequent step, as at 418. The method 400 may then loop back to receiving a walk command at 408.

In some embodiments, any of the methods of the present disclosure may be executed by a computing system. FIG. 9 illustrates an example of such a computing system 900, in accordance with some embodiments. The computing system 900 may include a computer or computer system 901A, which may be an individual computer system 901A or an arrangement of distributed computer systems. The computer system 901A includes one or more analysis module(s) 902 configured to perform various tasks according to some embodiments, such as one or more methods disclosed herein. To perform these various tasks, the analysis module 902 executes independently, or in coordination with, one or more processors 904, which is (or are) connected to one or more storage media 906. The processor(s) 904 is (or are) also connected to a network interface 907 to allow the computer system 901A to communicate over a data network 909 with one or more additional computer systems and/or computing systems, such as 901B, 901C, and/or 901D (note that computer systems 901B, 901C and/or 901D may or may not share the same architecture as computer system 901A, and may be located in different physical locations, e.g., computer systems 901A and 901B may be located in a processing facility, while in communication with one or more computer systems such as 901C and/or 901D that are located in one or more data centers, and/or located in varying countries on different continents).

A processor can include a microprocessor, microcontroller, processor module or subsystem, programmable integrated circuit, programmable gate array, or another control or computing device.

The storage media 906 can be implemented as one or more computer-readable or machine-readable storage media. Note that while in the example embodiment of FIG. 9 storage media 906 is depicted as within computer system 901A, in some embodiments, storage media 906 may be distributed within and/or across multiple internal and/or external enclosures of computing system 901A and/or additional computing systems. Storage media 906 may include one or more different forms of memory including semiconductor memory devices such as dynamic or static random access memories (DRAMs or SRAMs), erasable and programmable read-only memories (EPROMs), electrically erasable and programmable read-only memories (EEPROMs) and flash memories, magnetic disks such as fixed, floppy and removable disks, other magnetic media including tape, optical media such as compact disks (CDs) or digital video disks (DVDs), BLURAY® disks, or other types of optical storage, or other types of storage devices. Note that the instructions discussed above can be provided on one computer-readable or machine-readable storage medium, or alternatively, can be provided on multiple computer-readable or machine-readable storage media distributed in a large system having possibly plural nodes. Such computer-readable or machine-readable storage medium or media is (are) considered to be part of an article (or article of manufacture). An article or article of manufacture can refer to any manufactured single component or multiple components. The storage medium or media can be located either in the machine running the machine-readable instructions, or located at a remote site from which machine-readable instructions can be downloaded over a network for execution.

In some embodiments, computing system 900 contains one or more rig walking module(s) 908. In the example of computing system 900, computer system 901A includes the rig walking module 908. In some embodiments, a single rig walking module may be used to perform some or all aspects of one or more embodiments of the methods. In alternate embodiments, a plurality of rig walking modules may be used to perform some or all aspects of methods.

It should be appreciated that computing system 900 is only one example of a computing system, and that computing system 900 may have more or fewer components than shown, may combine additional components not depicted in the example embodiment of FIG. 9, and/or computing system 900 may have a different configuration or arrangement of the components depicted in FIG. 9. The various components shown in FIG. 9 may be implemented in hardware, software, or a combination of both hardware and software, including one or more signal processing and/or application specific integrated circuits.

Further, the steps in the processing methods described herein may be implemented by running one or more functional modules in information processing apparatus such as general purpose processors or application specific chips, such as ASICs, FPGAs, PLDs, or other appropriate devices. These modules, combinations of these modules, and/or their combination with general hardware are all included within the scope of protection of the invention.

The foregoing description, for purpose of explanation, has been described with reference to specific embodiments. However, the illustrative discussions above are not intended to be exhaustive or to limit the disclosure to the precise forms disclosed. Many modifications and variations are possible in view of the above teachings. Moreover, the order in which the elements of the methods described herein are illustrate and described may be re-arranged, and/or two or more elements may occur simultaneously. The embodiments were chosen and described in order to explain at least some of the principals of the disclosure and their practical applications, to thereby enable others skilled in the art to utilize the disclosed methods and systems and various embodiments with various modifications as are suited to the particular use contemplated. 

1. A method for moving a drilling rig, comprising: receiving, at a control system, a selection of a rig walking mode from a user via a control device, wherein the rig walking mode corresponds to a direction of movement; determining, using the control system, an angle of orientation for each foot of a plurality of feet of the drilling rig based on the selected rig walking mode, wherein the angles of orientation are coordinated so as to result in the rig moving in the direction of movement corresponding to the rig walking mode that was selected; rotating the feet by sending signals from the control system, such that the feet are in the angle of orientation; lifting the rig by pushing the feet into a ground; and moving the rig relative to the ground in the direction of movement.
 2. The method of claim 1, further comprising receiving a walk command after receiving the selection of the rig walking mode, wherein rotating the feet occurs in response to receiving the walk command.
 3. The method of claim 1, wherein rotating the feet comprises: receiving a feedback signal from a rotary position sensor coupled to a rotation mechanism configured to rotate one of the feet; and adjusting a rotation of the one of the feet in response to the feedback signal.
 4. The method of claim 1, wherein rotating the feet comprises reducing a rotation speed of the feet prior to reaching the angle of orientation.
 5. The method of claim 1, wherein the rig walking mode comprises rotating the drilling rig, and wherein rotating the feet comprises rotating at least one of the feet to a first angle and rotating at least another one of the feet to a second angle, the first and second angles being different by between about 1 degree and about 10 degrees.
 6. The method of claim 1, further comprising disabling individual control of the feet by the control device after receiving the selection therefrom, such that the feet are rotated to the angle of orientation without intervention from the user.
 7. A drilling rig system, comprising: a substructure; a plurality of walking pods coupled to the substructure, each of the walking pods comprising a rotating mechanism, a lift mechanism, a travel mechanism, and a foot, wherein the rotating mechanism is configured to rotate the foot relative to the substructure and a ground, the lift mechanism is configured to raise and lower the foot relative to the substructure and the ground, and the travel mechanism is configured to move the foot relative to the substructure and the ground in a horizontal direction; and a control system in communication with the plurality of walking pods, wherein the control system is configured to: receive a selection of a rig walking mode from a user via a control device, wherein the rig walking mode comprises a walking direction; automatically determine an angle of orientation for each foot based on the selected rig walking mode, wherein the angles of orientation are coordinated so as to result in the substructure moving in the walking direction of the rig walking mode that was selected; cause the respective rotating mechanisms to rotate the respective feet, such that each foot of the walking pods is in the angle of orientation that was determined for the respective foot; cause the respective lift mechanisms to lift the substructure by pushing the feet into the ground; and cause the travel mechanisms to move the substructure relative to the feet in the angle of orientation.
 8. The drilling system of claim 7, wherein the control system comprises a rig controller and a mobile control module, the mobile control module being in communication with the plurality of walking pods via the rig controller.
 9. The drilling system of claim 7, wherein the plurality of walking pods each comprise a rotary position sensor configured to provide a feedback signal to the control system representing a rotational position of the foot relative to the substructure.
 10. The drilling system of claim 9, wherein at least one of the rotation mechanisms comprises a slew drive, and wherein the rotary position sensor comprises an encoder coupled to the slew drive.
 11. The drilling system of claim 7, wherein the control system is configured to decrease a rotation speed of the feet prior to stopping rotation of the feet when the feet are in the orientation.
 12. The drilling system of claim 11, wherein the control system is configured to ramp the rotation speed down prior to stopping rotation.
 13. The drilling system of claim 7, wherein the travel mechanism comprises a horizontally-positioned hydraulic cylinder that is configured to slide the foot relative to the substructure.
 14. The drilling system of claim 7, wherein in at least one rig walking mode, the feet are all positioned at a first angle relative to a centerline of the substructure.
 15. The drilling system of claim 14, wherein in at least another rig walking mode, the predetermined orientation for at least one of the feet is a first angle, and the predetermined orientation for at least another one of the feet is a second angle, the first angle being different than the second angle, and wherein the walking direction in the at least one rig walking mode comprises a rotational direction.
 16. The drilling system of claim 15, wherein the first angle is between 1 degree and 10 degrees greater than the second angle.
 17. A method for moving a drilling rig, comprising: receiving a selection of a rig walking mode, wherein the rig walking mode corresponds to a direction of movement, and wherein the rig walking mode is selected from a plurality of rig walking modes, wherein each of the plurality of rig walking modes is associated with at least one angle of orientation for feet of the drilling rig; automatically determining, using the control system, a respective angle of orientation for each of the feet of the drilling rig based on the selected rig walking mode, wherein the angles of orientation are coordinated so as to result in the rig moving in the direction of movement corresponding to the rig walking mode that was selected; rotating the feet such that each of the feet are in the respective angle of orientation; lifting the rig by pushing the feet into a ground; and moving the rig relative to the ground in the direction of movement.
 18. The method of claim 17, wherein rotating the feet comprises: receiving a feedback signal from a rotary position sensor coupled to a rotation mechanism configured to rotate one of the feet; and adjusting a rotation of the one of the feet in response to the feedback signal.
 19. The method of claim 17, wherein the plurality of rig walking modes comprise: a first rig walking mode in which the angles of orientation are the same, such that the direction of movement is linear; and a second rig walking mode in which two of the angles of orientation are different from two others of the angles of orientation, such that the direction of movement is rotary.
 20. The method of claim 19, wherein, in the second rig walking mode, the two angles of orientation differ from the two other angles of orientation by between about 1 degree and about 10 degrees. 